The subject matter disclosed herein relates generally to imaging systems, and more particularly to methods and system for locating regions of interest in objects.
Localizing regions of interest, for example lesions, within medical images of subjects may be performed using image information from multiple imaging modalities. In some systems, image information from a Nuclear Medicine (NM) scan and an x-ray Computed Tomography (CT) scan may be used to locate a lesion within the patient. However, in NM-CT applications, although the CT image acquisition time is relatively short (e.g., 30 seconds to scan a region of interest), the acquisition of NM image information, for example, Single Photon Emission Computed Tomography (SPECT) is significantly longer (e.g., 20-30 minute acquisition time). Accordingly, conventional systems that acquire full SPECT emission data require a longer scan time in order to obtain the SPECT data.
Thus, known systems that use SPECT-CT for localizing regions of interest have long acquisition times, as well as an increased likelihood of motions artifacts in reconstructed images, such as due to patient motion. Additionally, repeated imaging scans also may be required, which increases the amount of injected radiopharmaceutical dose, thereby increasing the amount of radioactive exposure to the patient.
In contrast to SPECT imaging, which requires long acquisition time and yields a three-dimensional (3D) image, planar NM imaging requires much shorter acquisition time, but yields a two-dimensional (2D) image. The 2D images do not include the information on the absolute or exact 3D location of, for example a lesion, within the patient.
Moreover, while 3D anatomic imaging, such as CT or MRI is capable of showing the internal organs of a patient in great details, a radiologist observing such anatomical images, often cannot easily spot lesions such as cancer tumors due to the fact that the image may be rich in structures, and that the tumor may not have significant contrast relative to healthy tissue. In contrast, NM images, both planar and 3D images (known as SPECT) are characterized with high contrast, showing lesions as a location of high concentration of radiolabel pharmaceutical. However, NM images generally do not show the anatomy of the patient.
In order to locate a lesion, and to be able to correlate the location of the lesion relative to the internal anatomy of the patient, known methods use 3D anatomical images registered to 3D NM (SPECT) image. These methods allow overlaying the two types of images (using false colors), or by showing the images side by side, while allowing coordinated navigation within the two images at once. However, 3D NM imaging requires lengthy data acquisition as 3D NM imaging requires obtaining large numbers of NM projections. In contrast, planar NM imaging requires only a short acquisition time, but lacks depth information. Thus, when a radiologist identifies a lesion in a planar NM image, it is not easy for him or her to spot the location of that lesion on the 3D anatomical image.